Demography of the bonnethead shark, Sphyrna tiburo (Linnaeus, 1758), in the southeastern Gulf of Mexico

The bonnethead shark, Sphyrna tiburo, is one of the most abundant species in catches from the Gulf of Mexico, particularly from Campeche. It is mainly caught with gill nets and it is available throughout the year. A demographic analysis was carried out, incorporating the best available information about its life history, such as age at first maturity, fecundity, longevity, sex ratio (1:1) and age-specific natural mortality. The age and growth data used come from northern individuals of the Gulf of Mexico. The first run was done to obtain the demographic parameters under natural conditions. Other simulations varying age at first capture and incorporating fishing mortality were made to estimate the rate of change of the net reproductive rate (R0), generation time, intrinsic rate of increase and doubling time. Using an age-structured dynamic model, R0 was projected until the year 2010. The results of the simulations showed that S. tiburo has a higher reproductive potential than other sharks. This analysis will allow us to establish the management strategies for the fishery

Juvenile megamouth shark, Megachasma pelagios, caught off the Pacific coast of Mexico, and its significance to chondrichthyan diversity in Mexico

On 16 November 2006, a female juvenile megamouth shark, Megachasma pelagios, was caught off the coast of Mexico in the Pacific Ocean, near Sebastián Vizcaíno Bay. This specimen, that has informally been referred to as “Megamouth No. 38”, measured 2265 mm in total length. It represents the third smallest female recorded for this taxon and the first report of M. pelagios off the Pacific coast of Mexico. The specimen is formally described here with basic anatomical data, and some aspects of this megamouth shark are compared with those of previously reported M. pelagios specimens. The occurrence near Sebastián Vizcaíno Bay is significant because it further emphasizes the high elasmobranch diversity in the area that should be regarded as a key region for shark conservation.

Population expansion and genetic structure in Carcharhinus brevipinna in the southern Indo-Pacific

Background: Quantifying genetic diversity and metapopulation structure provides insights into the evolutionary history of a species and helps develop appropriate management strategies. We provide the first assessment of genetic structure in spinner sharks (Carcharhinus brevipinna), a large cosmopolitan carcharhinid, sampled from eastern and northern Australia and South Africa.\ud \ud Methods and Findings: Sequencing of the mitochondrial DNA NADH dehydrogenase subunit 4 gene for 430 individuals revealed 37 haplotypes and moderately high haplotype diversity (h = 0.6770 ±0.025). While two metrics of genetic divergence (Φ(ST) and F(ST)) revealed somewhat different results, subdivision was detected between South Africa and all Australian locations (pairwise Φ(ST), range 0.02717–0.03508, p values ≤ 0.0013; pairwise F(ST) South Africa vs New South Wales = 0.04056, p = 0.0008). Evidence for fine-scale genetic structuring was also detected along Australia's east coast (pairwise Φ(ST) = 0.01328, p < 0.015), and between south-eastern and northern locations (pairwise Φ(ST) = 0.00669, p < 0.04).\ud \ud Conclusions: The Indian Ocean represents a robust barrier to contemporary gene flow in C. brevipinna between Australia and South Africa. Gene flow also appears restricted along a continuous continental margin in this species, with data tentatively suggesting the delineation of two management units within Australian waters. Further sampling, however, is required for a more robust evaluation of the latter finding. Evidence indicates that all sampled populations were shaped by a substantial demographic expansion event, with the resultant high genetic diversity being cause for optimism when considering conservation of this commercially-targeted species in the southern Indo-Pacific